However the result of demodulation is often masked by noise containing in the measured signals 比较各段信号的异同以揭示故障齿的确切位置。

Usually series mode is used in low frequency circuit while bypass mode is used in high frequency circuit , series mode micro - switch with cantilever structure is similar to an fet , when voltage is applied on gate , and the fet will be turned on between source and drain 有静电电压作用在梁和底面电极时，梁发生偏转，在源极和漏极之间实现导通，常用于自控和通信系统的信号通路空气桥旁路开关主要用于微波段信号的通路。

In light of the limitation of fast fourier transform ( fft ) for the method of traditional spectrum analysis to analyze the unsteady signal , wavelet and wavelet analysis are made for the typical unsteady process signal of starting up and shut down with the good characteristic of simultaneous localization in both the time and the frequency domains based on the field test on the vibration of two - row placed units in lijiaxia hydropower station , in which the signal is decomposed into different frequency band , and then the weak signal is caught and the dominant frequency is picked up for the analysis of the vibration source 摘要基于李家峡水电站双排机组振动的现场试验研究，并且针对传统频谱分析方法傅立叶变换( fft )对于非平稳信号已力不从心这一缺陷，利用小波分析方法在时域和频域上同时具有良好的局部化性质，通过对开停机这一典型非平稳过程信号进行小波及小波包分析，将其分解到不同频带内，获取微弱信息和提取优势频率，并对其作振源分析，得出开停机初始时刻因水流不稳均出现强烈的振动现象，且低频段信号能量最大，开停机过程水流脉动压力和尾水涡带摆动是引起定子基础振动的主要原因。

After analysising three existed methods for phase difference correction on discrete spectrum , it is recommended to correct the spectrum containing small noise in engineer practice by the first phase difference correcting method ( performing fft analysis on two continuous original sequence ) with harming window 综合分析现有三种离散频谱相位差校正方法，推荐在小噪声工程实际中加hanning窗的第一种相位差法(采连续两段信号作相同点数fft的相位差校正法)进行校正。